Intrinsic magnetic properties of In2O3 and transition metal-doped-In2O3

This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In₂O₃. Undoped nanocrystalline In₂O₃ is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In₂O₃ samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit.     

Effects of In-substitution on the microstructure and magnetic properties of Bi-CVG ferrite with low temperature sintering

[Y_1.05Bi_0.75Ca_1.2](Fe_4.4−xIn_xV_0.6)O₁₂(In_x:Bi-CVG) ferrite material has been prepared successfully by a solid-state reaction method. The effects of In³⁺ substitution and sintering temperatures on the bulk density, microstructure and magnetic properties are performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), materials automatic test system (MATS) and microwave ferrite parameters meter. The results show that In³⁺ can lower the sintering temperatures and enhance the magnetic properties of Bi-CVG ferrite. Besides, all sintered specimens with different In³⁺ contents show a single garnet crystal structure. The specimen of [Y_1.05Bi_0.75Ca_1.2](Fe₄In_0.4V_0.6)O₁₂ sintered at 1075 °C shows homogenous distribution of grain size and densified microstructures. The ferromagnetic resonance linewidth (ΔH) has an increase with In³⁺ contents. Additionally, the sample has the optimum magnetic properties: ρ=5.23 g/cm³, B_r=31.3 mT, H_c=378.8 A/m, 4πM_s=506.2×10⁻⁴ T.     

Synthesis of corundum structure ITO nanocrystals by hydrothermal process at low pressure and low temperature

The corundum structures of In₂O₃:Sn (ITO) nanoparticles were synthesized by hydrothermal processing of InCl₃ and SnCl₄·5H₂O precursor at low temperature of 250 °C and 40 bar pressure for 3 h. The precursor was precipitated in a white gel of InOOH. After drying at 150 °C in air, it was crystallized in orthorhombic structure. InOOH powder was transformed into dark-gray rhombohedral In₂O₃ by sintering at 420 °C in forming gas for 1 h. The samples were characterized by means of XRD, SEM, and TEM. The particle size of the resulted ITO powder was about 32 nm.     

H2S-sensing properties of Pt-doped mesoporous indium oxide

Pt-doped mesoporous indium oxide (In₂O₃) has been successfully obtained by a simple and effective in situ nanocasting method. The resultant samples were characterized by XRD, FE-SEM, TEM, N₂ physisorption, XPS and EDX. The gas sensing properties for hydrogen sulfide (H₂S) of the Pt-doped mesoporous In₂O₃ specimens were also examined. The results exhibit those In₂O₃ specimens possess much higher response to H₂S even at low concentration of 2 ppm and a lower optimum working temperature of 150 °C. A possible mechanism was also provided to explain the improvement of the sensing properties.     

Effects of In-substitution on the structure and magnetic properties of multi-doped YIG ferrites with low saturation magnetizations

Multi-doped YIG ferrites {Y_1.7Gd_0.5Ca_0.8}[Fe_2−xIn_x](Fe_2.15V_0.4Mn_0.05Al_0.4)O₁₂ (x=0, 0.3, 0.6, 0.7, 0.8 and 0.9) with low saturation magnetizations (4πM_s=400-600 G at 298 K) were prepared by a conventional ceramic technology and the effects of In³⁺-substitution on their structures and magnetic properties were systematically investigated using XRD, SEM and VSM. It has been found that as-synthesized powders and sintered ferrites showed a single-phase of garnet structure with a cell parameter (a) that increased linearly with increase in In³⁺ concentration from x=0 up to 0.9. Apparent relative densities of sintered samples were all over 98%, but no remarkable influences of In³⁺-substitution were observed by SEM on the refinement of crystal grains and the enhancement of sintering of ferrites. In addition, the Curie temperature T_c decreased almost linearly as In³⁺concentration increased, while the corresponding saturation magnetization at room temperature presented a variation characterized by a gradual increase first and then a rapid plunge. On the basis of quantitative analysis of XRD data and the theory on super-exchange interactions, it has been established that the incorporated In³⁺ ions via doping were exclusively located at the sites with octahedral coordinations in the crystal structure and the aforementioned magnetic properties can be simply attributed to weakening super-exchange interactions between neighboring magnetic ions through oxygen ions due to the “dilution effect” of added non-magnetic In³⁺ ions.     

Magnetism due to oxygen vacancies and/or defects in undoped semiconducting and insulating oxide thin films

Room temperature ferromagnetism was observed in HfO₂, TiO₂, and In₂O₃ films grown on yttrium-stabilized zirconia, LaAlO₃, and MgO substrates, respectively. While the magnetic moment is rather modest in the case of In₂O₃ films, it is very large in the other two cases. Thin film form, which might create necessary defects and/or oxygen vacancies, must be the main reason for undoped semiconducting and insulating oxides to become ferromagnetic. From the results, a serious question arises if a transition-metal doping indeed plays any essential role in producing ferromagnetism (FM) in non-magnetic oxides.     

Effect of hydrogenation vs. re-heating on intrinsic magnetization of Co doped In2O3

Influence of Co doping for In in In₂O₃ matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co²⁺ ions are well incorporated at the In³⁺ sites in In₂O₃ lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In₂O₃ is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300 K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies V_o) or bound magnetic polarons around the dopant ions.     

Synthesis and characterization of V3O7⋅H2O nanobelts

V ₃O₇?H₂O nanobelts were prepared by a hydrothermal method at 190 ^°C using V ₂O₅?nH₂O gel and H₂C₂O₄?2H₂O as starting agents. The nanobelts obtained have diameters ranging from 40 to 70 nm with lengths of up to several micrometers. Their morphology and structure have been characterized by XRD, SEM, TEM and IR spectroscopy. The effect of the annealing temperature on the morphology of the resulting product has been investigated. XRD and SEM showed that thermal annealing of the V ₃O₇?H₂O sample in air led to the collapse of the V ₃O₇?H₂O nanobelt structure and the convert into V ₂O₅ nanobelts. For the first time V ₂O₅ nanobelts with an ultrahigh aspect-ratio have been obtained in air. Furthermore, electrical conductivity and static magnetic susceptibility measurements have been carried out.     

A close correlation between induced ferromagnetism and oxygen deficiency in Fe doped In2O3

We report on the reversible manipulation of room temperature ferromagnetism in Fe (5%) doped In₂O₃ polycrystalline magnetic semiconductor. The X-ray diffraction and photoemission measurements confirm that the Fe ions are well incorporated into the lattice, substituting the In³⁺ ions. The magnetization measurements show that the host In₂O₃ has a diamagnetic ground state, while it shows weak ferromagnetism at 300 K upon Fe doping. The as-prepared sample was then sequentially annealed in hydrogen, air, vacuum and finally in air. The ferromagnetic signal shoots up by hydrogenation as well as vacuum annealing and bounces back upon re-annealing the samples in air. The sequence of ferromagnetism shows a close inter-relationship with the behavior of oxygen vacancies (V_o). The Fe ions tend to a transform from 3+ to 2+ state during the giant ferromagnetic induction, as revealed by photoemission spectroscopy. A careful characterization of the structure, purity, magnetic, and transport properties confirms that the ferromagnetism is due to neither impurities nor clusters but directly related to the oxygen vacancies. The ferromagnetism can be reversibly controlled by these vacancies while a parallel variation of carrier concentration, as revealed by resistance measurements, appears to be a side effect of the oxygen vacancy variation.     

Microstructural and magnetic properties of Ax:Zn1-xO (A=Mn,Gd and Mn/Gd) nanocrystals

We report the microstructural and magnetic properties of transition (3d) and rare earth (4f) metal substituted into the A_x:Zn_1?xO (A=Mn, Gd and Mn/Gd) nanocrystal samples synthesized by solgel method. The structural properties and morphology of all samples have been analysed using X-ray diffraction (XRD) method and scanning electron microscopy. The impurity phase in the XRD patterns for all samples is not seen, except (Mn/Gd):ZnO sample where a very weak secondary phase of Gd₂O₃ is observed. Due to the large mismatch of the ionic radii between Mn²⁺ and Gd³⁺ ions, the strain inside the matrix increases, unlike the crystallite size decreases with the substitution of Mn and Gd into ZnO system. A couple of additional vibration modes due to the dopant have been observed in Raman spectrum. The magnetic properties have been studied by vibrating sample magnetometer. The magnetic hysteresis shows that Mn:ZnO and Gd:ZnO have soft ferromagnetic (FM) behaviour, whereas (Mn/Gd):ZnO has strong FM behaviour at room temperature (RT). The enhancement of ferromagnetism (FM) in (Mn/Gd):ZnO sample might be related to short-range FM coupling between Mn²⁺ and Gd³⁺ ions via defects potential and/or strain-induced FM coupling due to the expansion lattice by doping. The experimental results indicate that RTFM can be achieved by co-substitution of 3d and 4f metals in ZnO which can be used in spintronics applications.     

P-n codoping induced enhancement of ferromagnetism in Mn-doped In2O3: A first-principles study

We have performed first-principles density functional theory calculation in order to investigate the feasibility of “p-n codoping method” in improving magnetic property of In₂O₃ based diluted magnetic semiconductors. We find that the ferromagnetic state is favored in Mn-doped In₂O₃, and Sn doping can increase magnetic moment in Mn-doped In₂O₃. These findings are in line with our earlier experimental observation. Along with previous works, we now have enough evidences to support that p-n codoping is a valid method to improve magnetism of oxides based diluted magnetic semiconductors.     

Co-doped In2O3 thin films: Room temperature ferromagnets

Laser-ablated Co-doped In₂O₃ thin films were fabricated under various growth conditions on R-cut Al₂O₃ and MgO substrates. All Co:In₂O₃ films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μ_B/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In₂O₃ thin films has confirmed that doping few percent of magnetic elements such as Co into In₂O₃ could result in a promising magnetic material.     

Synthesis of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids

Fe₃O₄ nanoparticles were hydrothermally synthesized under continuous microwave irradiation from FeCl₃·6H₂O and FeSO₄·7H₂O aqueous solutions, using NH₄OH as precipitating reagent and N₂H₄·H₂O as oxidation-resistant reagent. The results of X-ray powder diffraction (XRD), FT–IR spectroscopy and scanning electron microscopy (SEM) measurements showed that the synthesized magnetite (Fe₃O₄) nanoparticles had an average diameter of 10 nm. The magnetic properties of the Fe₃O₄ nanoparticles were measured using a vibrating sample magnetometer (VSM), indicating that the nanoparticles possessed high saturation magnetization at room temperature. The Fe₃O₄ nanoparticles were used to prepare magnetic fluids (MFs) based on water, and the properties of the MFs were characterized by a Gouy magnetic balance, a capillary rheometer and a rotating rheometer, respectively.     

THE STRUCTURE AND MAGNETIC PROPERTIES OF La2-2xSr1Ca2xMn2O7 (x=0.25－1.00)

In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La_2-2xSr₁Ca_2xMn₂O₇ have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn³⁺/Mn⁴⁺ ratio and Jahn-Teller-type lattice distortion of MnO₆ octahedra due to the introduction of Ca²⁺ ions.     

Anomalous Hall effect in Cu and Fe codoped In2O3 and ITO thin films

We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In₂O₃ and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments M_r and coercive fields H_C are quite different. M_r and H_C values of ITO film are much smaller than that of In₂O₃. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In₂O₃ thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples.     

Co和Cr掺杂对层状钙钛矿锰氧化物La1.2Sr1.8Mn2O7磁性的影响

研究了层状钙钛矿锰氧化物La_1.2Sr_1.8Mn₂O₇中Mn被Co和Cr替代对磁性能的影响.Co替代Mn后,长程铁磁序被破坏,铁磁性减弱,出现团簇玻璃态和自旋玻璃态,表明Co离子和Mn离子之间不存在双交换作用.而Mn被Cr替代后长程铁磁序仍然保持,证实Cr³⁺和Mn³⁺之间存在铁磁性交换作用. 关键词：     

Large-scale synthesis of In2O3 nanowires

In₂O₃ nanowires have been successfully fabricated on a large scale from indium particles by thermal evaporation at 1030 °C. The as-synthesized products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images show that these nanowires are uniform with diameters of about 60–120 nm and lengths of about 15–25 μm. XRD and selected-area electron diffraction analysis together indicate that these In₂O₃ nanowires crystallize in a cubic structure of the bixbyite Mn₂O₃ (I) type (also called the C-type rare-earth oxide structure). The growth mechanism of these nanowires is also discussed. Received: 29 June 2001 / Accepted: 28 September 2001 / Published online: 20 December 2001     

Structure and physical properties of Li4Ti5O12 synthesized at deoxidization atmosphere

Powders of spinel Li₄Ti₅O₁₂ (LTO) were successfully synthesized at reducing conditions by solid-state method. The structure and physical properties of Li₄Ti₅O₁₂ were examined by X-ray diffraction (XRD), Raman spectroscopy, scanning electronic microscopy (SEM), and differential capacitance, respectively. XRD shows that both samples are single-phase spinel compounds. LTO synthesized in Ar/H₂(8% mol) has a larger lattice parameter than that in Ar. SEM indicates that all of the prepared powders have the uniform, nearly cubic structure morphology with narrow size distribution in the range of 200–300 nm. Raman spectra indicate that the Raman bands corresponding to the Ti–O vibration has a blue shift from 674 to 680 cm⁻¹ due to the few H₂ in the synthesized condition, indicating that there is very few oxygen vacancies in the Li₄Ti₅O₁₂ synthesized under Ar/H₂ (8% mol). The dQ/dV vs. voltage plots reveals the redox potentials for the synthesized Li₄Ti₅O₁₂-negative electrode materials.     

Tuning electronic properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires by doping control

We present two effective routes to tune the electronic properties of single-crystalline In₂O₃ nanowires by controlling the doping. The first method involves using different O₂ concentrations during the synthesis. Lightly (heavily) doped nanowires were produced by using high (low) O₂ concentrations, respectively, as revealed by the conductances and threshold voltages of nanowire-based field-effect transistors. Our second method exploits post-synthesis baking, as baking heavily doped nanowires in ambient air led to suppressed conduction and a positive shift of the threshold voltage, whereas baking lightly doped nanowires in vacuum displayed the opposite behavior. Our approaches offer viable ways to tune the electronic properties of many nonstoichiometric metal oxide systems such as In₂O₃, SnO₂, and ZnO nanowires for various applications. PACS 85.35.-p     

Effect of nanoparticles on the magnetic properties of Mn–Zn soft ferrite

In this paper, the effect of nanostructures on the magnetic properties like the specific saturation magnetization (σ_S) and the coercivity (H_C) for Mn_0.4Zn_0.6Fe₂O₄ ferrite prepared by the co-precipitation method has been presented. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanoparticles, and that the average size of these nanoparticles calculated with the Scherrer formula depends upon the sintering temperature. When the sintering temperature is increased from 500 to 900 °C, the average nanoparticle diameter varies from 19.3 to 36.4 nm. The nanoparticle phase is further confirmed by scanning electron microscopy (SEM). Both results are found to be in good agreement. The magnetic properties are explained on the basis of the single-domain and multi-domain theory.